Thermionic conversion of microwave energy to direct current



March 11, 1969 A. E. BLUME 3,432,590

THERMIONIC CONVERSION OF MICROWAVE ENERGY TO DIRECT CURRENT Filed Aug.51, 1966 Sheet of 2 INVENTOR} fl/arz E. Blame ATTORNEYS March 11, 1969A. E. BLUME 3,432,690

THERMIONIC CONVERSION OF MICROWAVE ENERGY 1'0 DIRECT CURRENT Filed Aug.31, 1966 Sheet 2 of 2 INVENTORI 6 /8/11 5. B/ume 7. A BY 25 pl- Z22 M5,1 ATTORNEYi United States Patent 3,432,690 THERMIONIC CONVERSION OFMICROWAVE ENERGY T0 DIRECT CURRENT Alan E. Blume, Scotia, N.Y., assignorto the United States of America as represented by the Secretary of theArmy Filed Aug. 31, 1966, Ser. No. 576,800

US. Cl. 310-4 4 Claims Int. Cl. H02n 11/00 ABSTRACT OF THE DISCLOSURE Adevice for converting microwave energy to direct current by use ofthermionic emission consisting of a waveguide having the inner surfacethereof lined with a lossy material whereby the microwave energyexciting the waveguide is converted intoheat and a refractory materialaffixed to the outside surface of the waveguide which serves as thecathode for a thermionic device. The refractory material when heatedemits electrons causing current to flow in the thermionic device.

This invention relates to devices for changing electromagnetic energy todirect current and more particularly to apparatus and method forconverting microwave energy to direct current by the use of thermionicemission.

An object of the invention is a converter means for changingelectromagnetic energy to direct current.

Another object of the invention is the utilization of microwave energyto heat the wall of a waveguide and by heat conduction activate thecathode of a thermionic converter attached thereto whereby a directcurrent is produced.

The invention will be more fully understood and its objects andadvantages further appreciated by referring now to the followingdetailed specification taken in conjunction with the accompanyingdrawings in the several figures of which like numerals identify likeelements and in which:

FIGURE 1 is an isometric view, partly in section, illustrating oneembodiment of the invention;

FIGURE 2 is a fragmentary sectional view taken along line 2-2 of FIGURE1; and

FIGURE 3 is a fragmentary longitudinal sectional view illustratinganother embodiment of the invention.

FIGURE 4 is a plan view of another embodiment of the invention utilizinga circular waveguide.

FIGURE 5 is a fragmentary sectional view taken along line 5-5 of FIGURE4.

In FIGURE 1 there is shown one form which my invention may take andwherein indicates a section of rectangular waveguide lined with a lossymaterial 11 such as carbon or a high resistance metal alloy. Block 38indicates a source of microwave energy for energizing waveguide 10. Theoutside surface 12 of the top wall 13 is provided with a layer of ametalloid oxide coating 14 such as beryllia which has a high electricalresistivity at 2000* C. to electrically isolate the waveguide 10 fromthe serially connected thermionic cells 15. Each thermionic cell 15consists of a cathode 16 of refractory material aflixed to the surfaceof the beryllia layer 14, a metallic anode 17 in spaced relationshipwith cathode 16 by means of insulator 18 so as to form a hermeticallysealed container having a chamber 19 containing cesium vapor 20 underlow pressure. An electrical conductor means 21 connects the anode of oneof the thermionic cells to the cathode of an adjacent thermionic cell toplace said cells in series connection. Lead 22 of the anode of the firstof said series connected cells and lead 23 of the cathode of the last ofsaid series connected cells provide means for connection to a load 24.It is to be understood that any number of such cells may be connected inseries or parallel in accordance with the electrical circuitrequirement. Further, it is also to be understood that the thermioniccells may be formed to completely embrace the peripheral surface of thewaveguide.

In operation microwave energy is fed into the waveguide 10, the innersurface of which is coated with the lossy material 11, whereby thewaveguide walls are heated and thus by heat conduction the cathode ofthe thermionic cell is heated causing it to emit electrons to obtain'acurrent flow in the cell and connected circuits.

In FIGURE 3 there is illustrated another embodiment of the inventionwherein waveguides formed with waveguide chokes are employed. In thisembodiment, a waveguide section 27 provided with a' flange at each endis coupled to a waveguide section 25 by means of a choke joint. Asindicated by waveguide sections 25 and 41 any number of waveguidesections may be coupled to each other through means of the waveguidechoke method. Waveguide section 27 is provided at one end with flange 29for coupling the waveguide to the source of microwave energy 38 and itsopposite end is also provided with a similar flange 28 for coupling toan adjacent waveguide. Waveguide section 25 is formed at one end with achoke plate 26 and coupled to waveguide section 27 by means of flange 28and choke plate 26 whereby a choke joint is formed. A spacer ring 33 ofinsulating material prevents electrical contact between choke plate 26and flange 28. The use of the choke joint eliminates the need forinsulation such as beryllia on the peripheral surface of the waveguides.Waveguide section '25 is also provided with a flange 30 for coupling towaveguide section 41 through choke plate 42 separated by a spacer ring33 as heretofore described in conjunction with the choke joint betweensections 27 and 25. Each of the waveguide sections are lined with lossymaterial 11. It is to be understood that in this embodiment of theinvention the waveguide utilized may for example consist of waveguidesection 27 and any number of waveguide sections such as sections 25 and41 coupled by means of choke joints as illustrated in FIG- URE 3 andwherein each of said sections carry a thermionic cell as described inthe following, resulting in a battery of series connected thermioniccells. Thermionic cells 32 are of substantially the same construction asthermionic cells 15 except that the edges of cathode 34 and anode 35 arehermetically sealed to insulator 36 comprising the vertical wall of thecell and whereby chamber is formed which contains the cesium vapor 20under low pressure. This constructing prevents shorting of the anode 35to the waveguide. Thermionic cells '32 extend between the flanges of thefirst section and between the choke joints and flanges of the respectiveadjacent sections of waveguides with their cathodes directly affixed tothe peripheral surfaces of the waveguide sections. An electricalconductor means 37 connects the anode of one cell to choke plate of theadjoining waveguide whereby the cells are connected in series. It isalso to be understood that the cells 32 may be of any geometricconfiguration and may completely embrace the peripheral surfaces of therelated waveguides.

In another embodiment of the invention, FIGURES 4 and 5, a circularwaveguide is employed. In particular, the use of the TE mode in thecircular waveguide is advantageous. Since there are no longitudinalcurrents accompanying this mode, the waveguide can simply be dividedinto longitudinal sections with a thin insulation between adjacentsections whereby the choke joints shown in FIGURE 3 are eliminated.Furthermore, the circumferential currents accompanying the TE mode inthe circular waveguide are constant with angle around the waveguide andthe heating of the waveguide will then not vary with angle resulting ina more uniform heating of the cathode of the thermionic converter. Now,with reference to FIGURES 4 and 5 wherein is shown the aforementionedembodiment and wherein for the purpose of illustration is shown acircular waveguide 45 divided into three sections 46, 47 and 48, itbeing understood that the waveguide may consist of any number ofsections. The ends of adjacent sections are separated by a thin ringinsulator spacer 56 adapted to fit the ends of the adjacent sections.The interior surfaces of the waveguide sections in this instance arealso coated with lossy material 11. The thermionic converter 53com-prises a cylindrical cathode 57 of refractory material adapted tofit the peripheral surface of cylindrical waveguide 45 and a concentriccylindrical metallic anode 58 which is held in spaced relationship tocathode 57 by means of insulator ring end closures 49 and 50 inhermetically sealed relationship with cathode 57 and anode 58 to formannular chamber 51 which contains cesium vapor 52. The length of eachthermionic converter may extend approximately the length of the relatedwaveguide section. To provide a battery of series connected thermionicconverters, and electrical conductor 54 bridges each of the relatedinsulator rings whereby the anode of one thermionic converter isconnected to the cathode of the adjacent thermionic converter. InFIGURES 3 and 5 the waveguide may serve as the cathode terminal andelectrical conductors 37 or 54 as the anode terminal when a singlethermionic converter is employed or conductors 37 or 54 of the anode ofthe last thermionic converter of a battery of series connectedthermionic converters may be utilized as the anode terminal.

While certain forms of the invention have been shown and described forthe purpose of illustration, it will be understood that modificationsmay be made in the practice of the invention without departing from thespirit or scope of the following claims. For instance, the powerconverted into heat will fall off exponentially, to a firstapproximation, with distance down the waveguide. To overcome this thediameter of the waveguide can be decreased or the resistivity of theinner surface metal can be increased.

I claim:

1. A device for generating direct current comprising in combination awaveguide, a source of microwave energy for energizing said waveguide, alossy material lining the inner surfaces of said waveguide, electricalinsulating means consisting of a metalloid oxide coating formed on theperipheral surfaces of said waveguide, a thermionic converter consistingof a cathode of refractory material and metallic anode elements spacedby means of a wall of insulating material to form a hermetically sealedchamber, cesium vapor in said chamber, said cathode being affixed tosaid metalloid oxide coating, electrical terminal means affixed in saidcathode, and electrical terminal means affixed in said anode.

2. The invention in accordance with claim 1 wherein said waveguide hasaffixed to said metalloid oxide coating a multiplicity of saidthermionic converters connected in series and longitudinally spaced fromeach other.

3. A device for generating direct current comprising in combination awaveguide consisting of a first waveguide section provided with a flangeat each end thereof, a series of waveguide sections, each of said seriesof waveguide sections provided with a choke plate at one end and aflange at the opposite end whereby a choke joint is formed between eachof said series of waveguide sections, the first of said series ofwaveguide sections being coupled to said first waveguide section throughthe choke plate thereof and a flange of said first waveguide sectionwhereby a choke joint is formed therebetween, a centrally perforatedinsulator spacer positioned between the choke plate and flange of eachof said choke joints preventing electrical contact between the flangeand choke plate of each of said choke joints, a lossy material liningthe inside surfaces of each of said waveguide sections, a thermionicconverter positioned between the flanges of said first waveguidesection, a thermionic converter positioned between the choke plate andflange of each of said series of waveguide sections, each of saidthermionic converters consisting of a continuous wall of insulationsupporting within its confines in hermetically sealed relationship acathode of refractory material in spaced relationship to an anode toform a chamber, cesium vapor in said chamber, the cathode of each ofsaid thermionic converters being affixed to the peripheral surface ofthe respective waveguide sections, electrical conductor means bridgingeach of said choke joints whereby the anode of one thermionic converteris connected to the cathode of the adjacent thermionic converter forminga battery of series connected thermionic converters, and microwaveenergy generating means coupled to said waveguide for exciting saidwaveguide.

4. A device for generating direct current comprising in combination acircular waveguide consisting of a number of circular waveguidesections, the adjacent ends of each of said waveguide sections spaced inbutted relationship by a thin ring insulator, a lossy material liningthe inner surfaces of each of said waveguide sections, a thermionicconverter encircling each of said waveguide sections intermediate theends thereof, each said thermionic converter comprising a cylindricalcathode of refractory material affixed to the peripheral surface of therelated waveguide section, a concentric metallic anode surrounding saidcathode, an insulator ring positioned at each end of said cathode andanode in hermetically sealed relationship therewith forming an annularchamber, and cesium vapor in said annular chamber, electrical conductormeans bridging each said thin ring insulator whereby the anode of onethermionic converter is connected to the cathode of the adjacentthermionic converter forming a battery of series connected thermionicconverters, and microwave energy generating means coupled to saidwaveguide for exciting said waveguide.

References Cited UNITED STATES PATENTS 2,563,573 8/1951 Baker 313-3103,041,543 6/1962 Papp 31539 3,196,295 7/1965 Oppen et a1. 3104 3,349,28210/1967 Krieger 315-94 FOREIGN PATENTS 1,002,537 8/1965 Great Britain.

MILTON O. HIRSHFIELD, Primary Examiner.

D. F. DUGGAN, Assistant Examiner.

US. Cl. X.R. 324-106; 333--81

